The present invention relates to a metal-based circuit board.
Conventionally, wiring ceramic substrates on which a circuit is formed and electronic components are mounted have been used. However, since such ceramic substrates have insufficient heat dissipation capacity for some applications, in order to provide a multilayer interconnection board with higher heat dissipation, a wiring substrate with a metal plate base, such as an aluminum plate, has been used in place of lo the ceramic substrates.
However, use of the metal plate has a problem that distortion and warpage develops due to heat generated by calcination etc. in a manufacturing process as it expands and contracts more easily due to heat than the insulating layer and the printed circuit formed on the substrate even though the metal plate has a higher heat dissipation capacity because it is made of a metal.
Laid-open Japanese Patent Application No. 5-327151, for example, discloses a conventional technology of a metal-based wiring substrate. JP 5-327151A discloses a metal-based circuit board having an improved insulator between a metal base and a conductive layer, which secures insulation while keeping heat dissipation capacity and prevents warpage and contortion of the metal base.
However, with the conventional metal-based circuit board, warpage of the metal plate could not be prevented completely since the base board is different in coefficient of thermal expansion from the printed circuit and the insulating layer formed on the base board. Moreover, there is another problem that the stress on the printed circuit and the metal plate generated through a heat cycle impairs the connection reliability between the printed circuit and the mounted components.
Furthermore, if forming a multilayered, printed circuit on a substrate is possible, the degree of freedom for circuit design may increase. However, distortion or warpage of the substrate may easily develop due to the multilayers, and disconnection may easily occur in the printed circuit.